Faulty Haldex Controller on a Mk1 TT 53 plate

The ESP light comes on intermittently (more often than not now) I'm told that it is the FWD controller unit is faulty (MOT Fail these days)and this is a Gen 1 box which is no longer available, only 2nd hand spares available on ebay.

My tech man has told me that I would need to replace the whole rear gearbox controller and all to fix this problem, however, someone else on my web search on this topic has told me that a gen 2 or later will not work with my ECU. Can anyone enlighten me on this subject as I was rather hoping to keep this car as a classic.

Thanks in advance